【作者】 李中华；

【导师】 张礼知；

【作者基本信息】 华中师范大学 ， 物理化学， 2017， 硕士

【摘要】 近年来,光催化技术以其较强的氧化能力和较好的环境亲和力,在能源开发与环境污染治理方面受到人们的广泛关注。传统的光催化主要是基于TiO2半导体光催化剂的研究。由于TiO2的禁带宽度较大,只能响应紫外光,而紫外光能量占太阳光总能量的不足5%。因此人们开始寻找具有可见光活性的新型半导体光催化材料。卤氧化铋(BiOX)拥有稳定的化学性质与独特的电子结构。BiOX在固氮、光解水产氢、环境污染治理等方面的研究多见于报道。在BiOX(X = Cl,Br,I)中,BiOCl的导价带氧化还原能力最强,但由于禁带宽度较大,BiOCl不能很好地利用可见光;BiOI对可见光的响应情况最佳,但其光生空穴氧化能力不足,又在一定程度上限制了 BiOI的光催化活性。在本论文中,我们以改善BiOCl、BiOI的可见光催化性能为目标,开展相关研究。首先,针对BiOCl的禁带宽度较大、不能很好地利用可见光的问题,我们以溶剂热法合成了表面具有氧空位的BiOCl,又以Fe掺杂的方式对BiOCl进行改性。密度泛函理论计算证明,Fe掺杂能够在BiOCl氧空位能级附近引入一条新的杂质能级。通过光催化固氮实验,我们发现Fe掺杂提高了 BiOCl可见光催化固氮的活性及循环性能。通过EPR、N2-TPD测试,我们认为BiOCl表面氧空位具有吸附活化N2的作用。DRS、光电流测试、荧光光谱等测试结果显示,Fe掺杂能够增强BiOCl在可见光区的响应情况、提高光生载流子的分离效率、改变BiOCl中电子跃迁途径。不仅限于氧空位上的电子,Fe掺杂BiOCl价带上的电子也能在可见光下发生跃迁,从而提供更多光生电子参与氮气的还原反应。因此,Fe掺杂含氧空位的BiOCl具有良好的可见光催化固氮效果。接下来,针对BiOI可见光吸收性能良好而光生空穴氧化能力不足的问题,我们以五氯酚钠为目标污染物,在BiOI可见光催化体系中引入过硫酸盐(PS)以加强光催化活性。BiOI/PS体系可见光降解五氯酚钠的速率常数达到BiOI的8倍。我们认为BiOI在可见光下产生的光生电子及·02-均能有效活化过硫酸盐,产生具有强氧化性的·SO4-和·OH。这些强氧化性自由基能极大增强BiOI可见光催化体系的氧化性,弥补BiOI光生空穴氧化能力的不足。随后,我们用GC-MS检测到了 2,3,5,6-四氯-1,4-苯二酚、3,4,5,6-四氯-1,2-苯二酚等五氯酚钠氧化降解的中间产物。因此,我们认为强氧化性的·SO4-和·OH通过加强对五氯酚钠的氧化脱氯过程,使BiOI在可见光下高效降解五氯酚钠。更多还原

【Abstract】 In recent years,the photo catalysis technology has been widely concerned in the developments of energy and environmental pollution control for its strong oxidation ability and good environmental affinity.The traditional photo catalysis is mainly based orn TiO2 semiconductor photocatalyst.Due to the wide band gap of TiO2,it can only absorb the ultraviolet light,whose energy is less than 5%of the total energy of the solar energy.So people begin to look for the new semiconductor photocatalytic materials with visible light activity.For the stable chemical properties and unique electronic structure,bismuth oxyhalides have attracted much attention in nitrogen fixation,photolysis of water for hydrogen production,environmental pollution control and etc.Among BiOX(X = Cl,Br,I),BiOCl has the strongest redox capacity,but it can’t make use of visible light because of the large band gap.Although BiOI has the best visible light absorption,the oxidation ability of its photogenerated holes is not good enough,which limits its photocatalytic activity to some extent.Through this study,we hope to make BiOCl,BiOI have better photocatalytic activity under visible light.Firstly,as BiOCl could not make use of visible light,we synthesized BiOCl with oxygen vacancy and improved its visible light performance in the form of iron doping.By density functional theory calculation,we found that there was a new impurity level near the oxygen vacancy level after iron-doped.Nitrogen fixation activity test under visible light showed that iron doping could promote the photocatalytic activity of BiOCl effectively.Then,the results of EPR and N2-TPD suggested that oxygen vacancies could adsorb and activate the nitrogen,DRS,p.hotocurrent and fluorescence spectrum indicated iron doping could enhance the response of BiOCl in the visible region,promove the separation efficiency of photogenerated carriers and change the transition way of electrons in BiOCl under visible light.More electrons could be excited and transferred from both oxygen vacancy and BiOCl valence level to involve in the reduction of nitrogen.Thus,Fe-doped BiOCl with oxygen vacancies had great photocatalytic activity during nitrogen fixation under visible light.Then,as BiOI had good visible-light response but poor redox ability,we used photocatalytic degradation of pentachlorophenol sodium as a typical photocatalytic reaction,and persulfate was introduced to enhance the photocatalytic activity at the same time.The rate constants of the degradation of sodium pentachlorophenate by BiOI/PS system were 8 times higher than BiOI.Under visible light,photo-induced electrons and·O2-could implement the process of persulfate activation to produce the strong oxidizing·SO4-and-OH which enhanced the oxidative capacity of reaction system greatly and made up for the poor redox ability of photogenerated holes.Then,many intermediates during the oxidative degradation of sodium pentachlorophenate were detected by GC-MS,such as 2,3,5,6-tetrachloro-1,4-benzenediol and 3,4,5,6-tetrachloro-1,2-benzenediol.Therefore,we believed that strong oxidative ·SO4-and ·OH improved the degradation efficiency of sodium pentachlorophenate with BiOI under visible light by enhancing the oxidative dechlorination process.更多还原